var Class = require('klasse');
var Texture = require('../Texture');


var FrameBuffer = new Class({

	/**
	 * Creates a new Frame Buffer Object with the given width and height.
	 *
	 * If width and height are non-numbers, this method expects the
	 * first parameter to be a Texture object which should be acted upon. 
	 * In this case, the FrameBuffer does not "own" the texture, and so it
	 * won't dispose of it upon destruction. This is an advanced version of the
	 * constructor that assumes the user is giving us a valid Texture that can be bound (i.e.
	 * no async Image textures).
	 *
	 * @class  FrameBuffer
	 * @constructor
	 * @param  {[type]} width  [description]
	 * @param  {[type]} height [description]
	 * @param  {[type]} filter [description]
	 * @return {[type]}        [description]
	 */
	initialize: function FrameBuffer(context, width, height, format) { //TODO: depth component
		if (typeof context !== "object")
			throw "GL context not specified to FrameBuffer";
	

		/**
		 * The underlying ID of the GL frame buffer object.
		 *
		 * @property {WebGLFramebuffer} id
		 */		
		this.id = null;

		/**
		 * The WebGLContext backed by this frame buffer.
		 *
		 * @property {WebGLContext} context
		 */
		this.context = context;

		/**
		 * The Texture backed by this frame buffer.
		 *
		 * @property {Texture} Texture
		 */
		//this Texture is now managed.
		this.texture = new Texture(context, width, height, format);

		//This is maanged by WebGLContext
		this.context.addManagedObject(this);
		this.create();
	},

	/**
	 * A read-only property which returns the width of the backing texture. 
	 * 
	 * @readOnly
	 * @property width
	 * @type {Number}
	 */
	width: {
		get: function() {
			return this.texture.width
		}
	},

	/**
	 * A read-only property which returns the height of the backing texture. 
	 * 
	 * @readOnly
	 * @property height
	 * @type {Number}
	 */
	height: {
		get: function() {
			return this.texture.height;
		}
	},


	/**
	 * Called during initialization to setup the frame buffer; also called on
	 * context restore. Users will not need to call this directly.
	 * 
	 * @method create
	 */
	create: function() {
		this.gl = this.context.gl; 
		var gl = this.gl;

		var tex = this.texture;

		//we assume the texture has already had create() called on it
		//since it was added as a managed object prior to this FrameBuffer
		tex.bind();
 
		this.id = gl.createFramebuffer();
		gl.bindFramebuffer(gl.FRAMEBUFFER, this.id);

		gl.framebufferTexture2D(gl.FRAMEBUFFER, gl.COLOR_ATTACHMENT0, tex.target, tex.id, 0);

		var result = gl.checkFramebufferStatus(gl.FRAMEBUFFER);
		if (result != gl.FRAMEBUFFER_COMPLETE) {
			this.destroy(); //destroy our resources before leaving this function..

			var err = "Framebuffer not complete";
			switch (result) {
				case gl.FRAMEBUFFER_UNSUPPORTED:
					throw new Error(err + ": unsupported");
				case gl.INCOMPLETE_DIMENSIONS:
					throw new Error(err + ": incomplete dimensions");
				case gl.INCOMPLETE_ATTACHMENT:
					throw new Error(err + ": incomplete attachment");
				case gl.INCOMPLETE_MISSING_ATTACHMENT:
					throw new Error(err + ": missing attachment");
				default:
					throw new Error(err);
			}
		}
		gl.bindFramebuffer(gl.FRAMEBUFFER, null);
	},


	/**
	 * Destroys this frame buffer. Using this object after destroying it will have
	 * undefined results. 
	 * @method destroy
	 */
	destroy: function() {
		var gl = this.gl;

		if (this.texture)
			this.texture.destroy();
		if (this.id && this.gl)
			this.gl.deleteFramebuffer(this.id);
		if (this.context)
			this.context.removeManagedObject(this);

		this.id = null;
		this.gl = null;
		this.texture = null;
		this.context = null;
	},

	/**
	 * Binds this framebuffer and sets the viewport to the expected size.
	 * @method begin
	 */
	begin: function() {
		var gl = this.gl;
		gl.viewport(0, 0, this.texture.width, this.texture.height);
		gl.bindFramebuffer(gl.FRAMEBUFFER, this.id);
	},

	/**
	 * Binds the default frame buffer (the screen) and sets the viewport back
	 * to the size of the WebGLContext.
	 * 
	 * @method end
	 */
	end: function() {
		var gl = this.gl;
		gl.viewport(0, 0, this.context.width, this.context.height);
		gl.bindFramebuffer(gl.FRAMEBUFFER, null);
	}
});

module.exports = FrameBuffer;